Hello, ticketyboo, and welcome.
Re. the internet via T.V., do I take it that it's already a very settled thing that your mum is just NOT going to want to deal with a computer? (Not being snarky, 'cos my own mum won't touch a computer).
I don't know anything about Bush TV but it sounds as though you have already looked at that at don't like it.
NTL offers internet via TV for £7.50 per month
ntl:home | Internet via TV - No Computer Needed! UK Broadband ISP
OR the Amstrad e-mailer thing might work
Amstrad E3 E-m@iler Superphone
Wouldn't a mobile 'phone help? Although I suppose she would only get tiny wee pictures.